1. Field of the Invention
The present invention relates generally to an electronic solid state programmable load and more particularly to a combining network for multiple PIN diode arrays having high power handling capabilities.
2. Background Description
It is desirable in the construction of microwave load dependent devices and circuits to provide a terminating load comprising a tuner, attenuator or phase shifter. Such loads allow measurements to be performed on the circuit. In this manner, noise-figure and gain circle data can be determined. The measurement of noise parameters utilizing an active load pull approach is discussed generally in Froelich, Automated Tuning for Noise Parameter Measurements Using a Microwave Probe, Microwave Journal, March, 1989, pp 83-96.
One form of tuner for providing a load to a circuit according to an active load pull approach is disclosed in U.S. Pat. No. 5,034,708, the teachings of which are expressly incorporated by reference herein. By providing an array of PIN diodes or similar solid state switching devices, a variable load can be constructed for use with a microwave load dependent device or circuit.
An array of PIN diodes can be adjusted to provide a desired load or impedance by providing a variable bias to predetermined of the diodes in the array so that the impedance of the predetermined diodes can be varied allowing the generation of a great number of desired impedance states for the overall array.
This type of diode array has disadvantages when used with high power circuits. "High power" in this instance means greater than 7 Watts. Traditionally, variable loads for such high power applications have been provided by means of a mechanical tuner that allows impedance to be varied by hand. Such mechanical tuners are, however, relatively slow and large. Mechanical tuners also tend to drift so that repeatability of measurements is difficult. For these reasons, mechanical tuners are not desirable for performing measurements of circuits formed on semi-conductor or similar wafers in which small size and high accuracy is necessary.
In view of the disadvantages of the prior art, this invention has as one object providing a high power solid state load for active load pull applications.
It is another object of this invention to provide a high power solid state load with variable impedance characteristics over a wide range of settings.
It is yet another object of this invention to provide a solid state load that is relatively small and capable of accurate repeatability of impedance measurement.